when the fire police got there the building was on fire,but

问题描述:

when the fire police got there the building was on fire,but on one knew
when the building ____ fire.A had caught B caught A还是 B,请指教
1个回答 分类:英语 2014-12-04

问题解答:

我来补答
B 有过去的时态为跳板才可以出现过去完成时!如By the time I arrived at the building,it had caught fire!
 
 
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